Polarized hydroxyapatite films and methods of making and using same

Abstract

Polarized hydroxyapatite films disposed on a substrate. The films have a residual polarization of at least 5 mC/cm2. Also provided are methods of making and using polarized hydroxyapatite. The films can be used as coatings of medical devices, such as, for example, medical implants.

1 ) A polarized hydroxyapatite film disposed on a substrate, the film comprising a plurality of rod-shaped crystals having a crystallographic c-axis substantially normal to the substrate and the film having a residual electrostatic charge of at least 5 mC/cm 2 . 
     
     
         2 ) The polarized hydroxyapatite film of  claim 1 , wherein the film has a gradient composition. 
     
     
         3 ) The polarized hydroxyapatite film of  claim 1 , wherein the film has a thickness of 100 nm to 50 microns. 
     
     
         4 ) The polarized hydroxyapatite film of  claim 1 , wherein the substrate is a metal substrate, a metal alloy substrate, or graphite substrate. 
     
     
         5 ) The polarized hydroxyapatite film of  claim 1 , wherein the substrate is an artificial hip, artificial spine, artificial neck, artificial elbow, artificial femur, artificial knee, artificial shoulder, artificial arm, artificial finger, screw, pin, rod, or a portion thereof. 
     
     
         6 ) The polarized hydroxyapatite film of  claim 1 , further comprising a plurality of metal nanoparticles disposed on at least a portion of a surface of the film. 
     
     
         7 ) A method of making a film disposed on substrate, the film comprising polarized hydroxyapatite, comprising the steps of:
 a) heating a precursor solution comprising a calcium precursor (e.g., calcium chloride), a phosphate precursor (e.g., potassium phosphate), and, optionally, sodium chloride buffered to a pH of 3 to 11, to a temperature of 50° C. to 100° C.; and   b) applying an electric current at a current density of 1 to 300 mA/cm 2  to the precursor solution after reaching the desired reaction temperature a);   
       such that the film comprising polarized hydroxyapatite comprising a plurality of hydroxyapatite crystals having the crystallographic c-axis of the hydroxyapatite is substantially normal to the substrate, the film having a residual electrostatic charge of at least 5 mC/cm 2 , is formed. 
     
     
         8 ) The method of  claim 7 , further comprising contacting the film from b) with a metal salt solution such that metal nanoparticles are formed and disposed on at least a portion of the surface of the film. 
     
     
         9 ) The method of  claim 7 , wherein the electric current is applied to the precursor solution for 0.1 minutes to 30 minutes. 
     
     
         10 ) The method of  claim 7 , further comprising heating the film from b). 
     
     
         11 ) The method of  claim 10 , wherein an electric field of greater than 1 kV/cm to 100 kV/cm is applied to the film during at least a portion of the heating. 
     
     
         12 ) The method of  claim 7 , further comprising:
 c) depositing a plurality of hydroxyapatite crystals by hydrothermal deposition on the film from b); and   d) optionally, doping the hydroxyapatite crystals during deposition by hydrothermal crystallization with cations, anions, or a combination thereof.   
     
     
         13 ) The method of  claim 9 , further comprising contacting the film from b), c), or d) with a metal salt solution under electrochemical reduction conditions such that metal nanoparticles are formed and disposed on at least a portion of the surface of the film. 
     
     
         14 ) The method of  claim 13 , wherein an electric field of 1 kV/cm to 100 kV/cm is applied to the film during at least a portion of the heating. 
     
     
         15 ) A device comprising the hydroxyapatite film of  claim 1 . 
     
     
         16 ) The device of  claim 15 , wherein the device is a medical implant, electret, or filter. 
     
     
         17 ) The device of  claim 16 , wherein the medical implant is an artificial hip, artificial spine, artificial neck, artificial elbow, artificial femur, artificial knee, artificial shoulder, artificial arm, artificial finger, screw, pin, rod, or a portion thereof. 
     
     
         18 ) A method of growing hydroxyapatite using a film of  claim 1  comprising exposing the film of  claim 1  to body fluid or simulated body fluid such that additional hydroxyapatite is deposited on the film of  claim 1 . 
     
     
         19 ) The method of growing hydroxyapatite of  claim 18 , wherein the method is carried out in vitro or in vivo.